feat: SessionLifecycleManager — auto-detect and repair dead tmux sessions

- Add internal/lifecycle/manager.go with Manager struct, Run() ticker loop
  (15s interval), EnsureAllSessions() for boot-time session creation, and
  reconcile() that recreates idle sessions and recovers working ones via
  SetFailed + CreateSession
- Add state.SetFailed() to record crash timestamp on SessionState
- Add internal/lifecycle/manager_test.go with mock tmux client and 3 tests:
  TestReconcileCreatesDeadSession, TestReconcileRecoversCrashedSession,
  TestEnsureAllSessions — all pass
- Wire lifecycle.Manager into cmd/claude-failover/main.go after state init

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/api/server.go

@@ -0,0 +1,41 @@
+// Package api exposes the HTTP control-plane used by the MCP gateway
+// and the orchestrator dashboard.
+package api
+
+import (
+	"fmt"
+	"net/http"
+
+	"forge.secuaas.ovh/olivier/claude-failover/internal/state"
+)
+
+const version = "0.1.0"
+
+// Server is a minimal HTTP server exposing /health and /status.
+type Server struct {
+	addr  string
+	state *state.State
+}
+
+// New creates a Server listening on addr.
+func New(addr string, s *state.State) *Server {
+	return &Server{addr: addr, state: s}
+}
+
+// Start registers routes and begins serving. Blocks until the listener fails.
+func (s *Server) Start() error {
+	mux := http.NewServeMux()
+	mux.HandleFunc("/health", s.handleHealth)
+	mux.HandleFunc("/status", s.handleStatus)
+	return http.ListenAndServe(s.addr, mux)
+}
+
+func (s *Server) handleHealth(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/json")
+	fmt.Fprintf(w, `{"status":"ok","version":%q}`, version)
+}
+
+func (s *Server) handleStatus(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/json")
+	w.Write(s.state.JSON())
+}